The antipruritic effect of acupuncture on serotonin-evoked itch in rats

The antipruritic effect of acupuncture was studied using a rat model of hindlimb scratching. After acupuncture or electroacupuncture (EA), which was conducted for 30 min, itch-associated behavior was induced by an intradermal injection of 2% serotonin (20 microl) into the rostral back, and then numbers of scratching bouts were counted for 60 min. During the first experiment, acupuncture stimulations were applied to several different points. However acupuncture significantly reduced numbers of scratchings only when applied to cervical dermatomes. In the second experiment, plain acupuncture, or 2Hz, or 120Hz EA were applied to acupoints LI 11 and LI 4, at which acupuncture stimulation produced the greatest antipruritic effect in the 1st experiment, and as serotonin was administered in the same manner described for the 1st experiment. Results showed that 2Hz EA stimulation tended to increase pruritic bouts by approximately 18% versus the animals treated with plain acupuncture, whereas 120Hz EA stimulation tended to decrease pruritic bouts by approximately 39% compared with animals subjected to plain acupuncture. When nor-binaltorphimine (a kappa-opioid receptor antagonist) was pretreated to elucidate the relation between kappa-opioid receptor and the antipruritic effect of 120Hz EA, it was found to markedly inhibit the antipruritic effect of 120Hz EA. These results suggest that acupuncture and EA stimulation are effective treatments for pruritus if administered to dermatomes corresponding to affected sites or to adjacent dermatomes and that this effect is due to the antipruritic effect of kappa-opioid receptor activation maximally induced by high-frequency EA stimulation.